The present invention relates to a polishing composition mainly used in polishing of a semiconductor wafer and to a polishing method using the polishing composition.
Polishing of a semiconductor wafer such as a silicon wafer is usually divided into at least two stages, preliminary polishing and finish polishing. Of these, preliminary polishing is further divided into two or more stages for the purpose of high quality and efficiency. As a polishing composition usable for finish polishing, a polishing composition described in Japanese Laid-Open Patent Publication No. 02-158684 is known, for example. The polishing composition of the publication comprises water, colloidal silica, a water soluble polymer such as polyacrylamide and sizofiran, and a water soluble salt such as potassium chloride.
In recent years, as design rules for semiconductor devices have required thinner devices, there is a demand for reducing small size LPDs (light point defects), which had not been considered problematic but are now considered to affect the performance of a semiconductor device. An LPD is a kind of defect observed on the surface of a wafer polished by using a polishing composition. Specifically, LPDs with a size of 0.12 μm or larger had been mainly considered problematic, which were caused by particles attached to wafer surfaces. Thus, an improvement in washing technique has largely reduced such LPDs. However, LPDs with a size smaller than the above (>0.065 μm) are mainly caused by scars occurring on wafer surfaces during preliminary polishing, in other words attributable to the polishing process. In many cases, these cannot be removed by finish polishing or washing. In this regard, even when the polishing composition described in Japanese Laid-Open Patent Publication No. 02-158684 is used for finish polishing, the number of LPDs attributable to the polishing process cannot be reduced more than before.